Known headrests provided for a vehicle seat include a manually operated height-adjusting mechanism. Adjusting a headrest to an appropriate height before beginning to drive is important for a user in terms of safety in the eventuality of a collision. However, when, after once adjusting the height of a headrest, the initial user of a vehicle sits down again in the same seat, this person may not notice that the position of the headrest has in the meantime been changed by another user of the same vehicle. Moreover, even when an initial user notices that the position of the headrest has changed, there is a tendency for such a person to use the seat as he/she finds it, without readjusting the height of the headrest, simply because it is too much bother to adjust the height every time that the user uses the seat.
On the other hand, before starting to drive a vehicle drivers usually adjust the position of the seat in a longitudinal direction in order to adjust the seat to their own driving positions. This positioning of a seat in a longitudinal direction is carried out with considerably greater frequency than the adjustment of the headrest mentioned above. It follows from this that if the height of the headrest can be adjusted automatically in conjunction with the positional adjustment of the vehicle seat, a procedure which a user almost invariably performs, the above-mentioned problem can be virtually solved.
In connection with the foregoing, a known vehicle seat having a headrest which moves in accordance with the sliding movement of the seat is described in JPH07-34761Y.
According to the construction described in JPH07-34761Y, a headrest is always biased by a spring to move upward over a seatback, and the headrest is connected to the lower rails of a sliding mechanism fixed by means of wire to a vehicle floor. In a case where a user with a smaller physique sits in the seat, the user moves the seat forward by means of the sliding mechanism. In this case, the wire pulls the headrest downward against the biasing force of the spring. On the other hand, in a case where a user with a larger physique sits in the seat, the user moves the seat backward by means of the sliding mechanism. In this case, the wire is loosened, and pulls up the headrest by the biasing force of the spring. Thus, upward and downward movement of the headrest and the sliding movement of the seat take place in conjunction with one another.
However, a headrest is generally provided on the top of a seatback with stays serving as supporting members. The stays are, for example, slidably positioned in a cylindrical guiding member provided at a frame of the seat. Thus, the user can adjust the headrest to a favorable height, by moving the stays upward and downward, and by fixing with a stopper provided at the guiding member.
Notwithstanding the advantages of the structures described in the known vehicle seat, with the construction of the vehicle seat described in JPH07-34761Y, frictional resistance between the stay and the guiding member has occasions assumed significance because of dimensional inaccuracies. For example, with the construction described in JPH07-34761Y, in a case where frictional resistance between the stays and the guiding member is greater than the biasing force of the spring, the headrest cannot be moved smoothly, and thus can cause problems with the operation of the headrest device.
Moreover, a further problem is that even when appropriate seat positions in a longitudinal direction are the same, the heights of the head positions of a taller person in a seated position and of a shorter person in a seated position can be different. Nonetheless, with the construction of the vehicle seat described in JPH07-34761Y, depending on the physique of the users, an appropriate height of the headrest cannot always be achieved, because the height of the headrest is uniformly determined in accordance with the position of the seat in a longitudinal direction.
A need thus exists for a headrest device, which not only, by means of a sliding mechanism, automatically and smoothly positions the height of the headrest of a vehicle seat in accordance with the position of the seat in a longitudinal direction, but which users can also individually and manually adjust to their own liking, in order to rectify unsuitable positions in the height of a headrest caused by differences in the physical characteristics of persons occupying the seat. The present invention has been made in view of the above circumstances and provides such a headrest device.